A typical dissolved air flotation device is illustrated in FIG. 1. This system comprises of an inlet chamber, a contact zone, a separation zone, and an effluent chamber. The contact zone further includes a micro-bubble injection installation near the device floor. The micro-bubble injection installation typically consists of micro-bubble generating nozzles installed on a nozzle header. The nozzle header receives pressurized liquid saturated with air and distributes it evenly to each nozzle. As the liquid passes the nozzles, micro-bubbles are generated. Furthermore, a micro-bubble injection installation may consist of multiple nozzle headers.
The inlet zone equalizes the incoming flow. The micro-bubbles injected at the bottom of the contact zone attach to the suspended particulates. A well designed contact zone promotes the collision of micro-bubbles with the suspended particles. The inclination of the inlet baffle increases the contact zone area from bottom to top. The increase in contact zone area reduces the flow velocity and therefore turbulence. The particles with one or more micro-bubbles attached, rise to the surface as the liquid flows to the separation zone. The rise of particulates to the surface is accomplished by enhancing the buoyancy via attachment of one or more micro-bubbles. The liquid devoid of suspended particulates and other impurities is removed from the bottom of the separation zone.
The depth of dissolved air flotation installations operating at high surface loading rates is known to be typically more than 4.0 m. Increased depth is known to provide process advantage in terms of clarification efficiency by altering the flow path in the separation zone. However, increased depth also results in high construction costs and maintenance costs.
An example of a dissolved air flotation system is illustrated in U.S. Pat. No. 3,175,687 to Jones. Jones '687 illustrates a flotation tank within which flotation is carried out to form a layer of sludge or float on top of the water within the tank. Aerated water is delivered to the bottom of the tank via a plurality of admission fittings that are disposed lengthwise along the bottom of the tank. A valve is associated with each admission fitting to selectively render the fitting operable or inoperable.
Yet another example of a clarification system is disclosed in U.S. Pat. No. 5,047,149 to Vion. Vion '149 discloses an apparatus for the clarification of liquids such as water. The apparatus includes a feature whereby flotation equipment is placed above an assembly for the pretreatment of the liquid. This allows a hydraulic balance to be brought to the various constitutes of the apparatus. This, in turn, allows for a small upstream load and the recycling, by simple gravity, of the floating particles collected at the surface of the flotation equipment.
A further clarification system is disclosed in U.S. Pat. App. 2009/0211974 to Bonnelye. Bonnelye '974 discloses a water clarifying device including a flotation zone, a membrane-based filtering zone, and an extracting means. The membranes are fed with floated water from down upwards in both the filtering phase and the backwashing phase.
There are significant drawbacks to know clarification systems to be implemented at high loading rates, such as the one illustrated in FIG. 1. Namely, the path between the contact zone and the effluent collection zone is often too short to ensure the removal of all of the agglomerated impurities. As illustrated in the system of FIG. 1, the path between the contact and effluent zones can be a straight line thereby reducing the time for which the liquid containing micro-bubbles is retained in the separation zone. The result of which is the lowermost agglomerated particles receive insufficient flotation time and are thus prevented from floating to the top for removal at the sludge collection chamber. As a result, bubble-particle agglomerates with lower flotation velocities are often carried along with the flow and delivered into the effluent zone. Another drawback concerns the acceleration of flow at the inlet of the effluent zone. This acceleration is often too great and results in the agglomerated particles being dragged into the effluent zone. Both of these drawbacks result in impurities being contained within the effluent.
The DAF devices of the present disclosure seek to overcome these drawback by both increasing the pathway the agglomerated particles must travel within the separation zone—thus permitting additional time for bubble-particle agglomerates with lower flotation velocities to rise to surface and separate, and decreasing the drag at the entrance to the effluent zone. The result is an increase in agglomerated particles that are removed via the sludge collection chamber and a corresponding decrease in impurities found within the effluent. There also exists a need in the art for a dissolved air flotation installation capable of operating at high loading rates that does not require excessive depth to improve the clarification efficiency. Further, there is also a need in the art for a dissolved air flotation system that is more cost effective and the design is capable of being easily incorporated in the existing conventional installations to increase the clarification capacity. The present invention is aimed at fulfilling these and other needs.